This invention relates to an engine having one or more cylinders with two intake or two exhaust valves wherein one of either the intake or exhaust valves may be retarded relative to the other respective intake or exhaust valve to control swirl motion of gases in the cylinder.
Swirl motion of gases in cylinders of engines can be used to improve engine performance and reduce emissions. xe2x80x9cSwirlxe2x80x9d refers to the gas flowing in a circular path in the cylinder under certain conditions. Swirl can be generated by gas flow from intake ports and exhaust ports. Intake flow for diesel and direct injection spark ignition engines is air. Intake flow for conventional port fuel injection spark ignition engines is an air/fuel mixture.
In conventional spark ignition engines at low loads, swirl improves combustion and fuel economy. On the other hand, in spark ignition engines at high load, swirl can increase knock tendency. At high engine speeds and loads, it is preferable to reduce swirl to minimize knock. In addition, creating additional swirl during the exhaust process can improve mixing and reduce NOx emissions.
In diesel engines, strong swirl at light loads and low engine speeds tends to reduce particulate emissions. Reduced swirl at high loads tends to reduce NOx emissions.
With direct injection spark ignition engines that are currently being developed, swirl improves engine combustion and performance at low and intermediate loads. But at high loads, swirl should be minimized to avoid maximum power output deterioration. However, in a direct injection spark ignition engine with late fuel ignition at light load, excessively strong swirl can reduce combustion stability and increase hydrocarbon emissions. At high engine speeds and at full load, swirl reduction is desirable to reduce combustion noise.
It should be readily appreciated that it would be desirable to control swirl to meet conflicting engine operation requirements. Engine efficiency, power output, noise and vibration and NOx emissions are all impacted by the strength of swirl of gases in an engine""s cylinders.
Prior art approaches to control swirl have proposed the use of a swirl port in conjunction with a normal intake port. One example of such a prior art approach is disclosed in U.S. Pat. No. 5,309,880, which is assigned to the assignee of the present invention. While this is a generally acceptable approach, a complex dual intake port system must be provided which may reduce maximum power output. This patent also requires a secondary throttle valve located in the secondary passage to provide control according to an engine control strategy.
These and other problems and shortcomings of the prior art are addressed by the present invention as summarized below.
According to the present invention, an internal combustion piston engine is provided that has plural intake ports or exhaust ports that are opened at different times or to a different extent to control swirl in the combustion chamber of intake gases or residual gases depending upon predetermined engine operation parameters and a combustion control strategy.
According to the invention, an internal combustion piston engine is provided that has at least one combustion chamber bounded by a cylindrical wall, a top portion of a reciprocating piston, and a cylinder head. To control intake gases, at least two intake ports may be formed in the cylinder head with each intake port providing an opening into the combustion chamber. A plurality of intake valves are each associated with one of the intake ports. A plurality of valve actuators cooperate with the intake valves to enable the intake valves to be selectively opened and closed during engine operation. Opening and closing of intake valves is controlled according to a time/lift schedule wherein either the time of opening of the valves may be controlled or the degree to which one of the valves is opened is controlled. The controller operates with at least one of the actuators varying the time/lift schedule of at least one of the intake valves relative to another one of the intake valves. The time/lift schedule is responsive to engine operating conditions to vary intake swirl as engine operating conditions vary.
In accordance with the present invention, one intake valve may be retarded relative to the other one of the intake valves to increase intake swirl when the engine is operating at low speed and under low load conditions.
Swirl can also be controlled by varying the extent to which an intake valve is lifted or by modifying the timing of the opening of the intake valves. According to the invention, one intake valve may be opened to a lesser extent relative to the other one of the intake valves to increase intake swirl when the engine is operating at low speeds and under low load conditions.
The time/lift schedule may control the time that one intake valve opens so that it is substantially simultaneous relative to the other intake valve, for instance, when the engine is operating at high speed and under high load condition to minimize swirl. The time/lift schedule can also control the timing of opening one intake valve so that it is retarded relative to the other intake valve at lower speeds and under lower load conditions to increase swirl.
According to another aspect of the present invention, an intake system for an engine having a plurality of combustion chambers each containing a piston is provided. At least three valves are provided per combustion chamber with at least two of the valves being intake valves and at least one of the valves being an exhaust valve. Actuators are provided for opening and closing the valves. A control device retards opening of one of the intake valves relative to another of the intake valves for the same combustion chamber to increase intake swirl ratio.
The invention may also be extended to increase swirl of residual gases in the combustion chamber by providing a plurality of exhaust valves that are opened at different time intervals or to a different extent to increase the swirl of residual gases in the combustion chamber. By increasing swirl of residual gases, improved mixing of the residual gases and the reduction of NOx emissions may be achieved. Retarding the opening of one of the exhaust valves may also be used to increase thermal efficiency.
According to the present invention, a method of controlling swirl in a combustion chamber of an engine is provided in either the intake gases or residual gases. According to the method, either two intake ports or two exhaust ports may be opened and closed at controlled time intervals so that either a first intake valve or first exhaust valve opens at a different time from a second intake valve or second exhaust valve to modify the amount of swirl created in the intake or exhaust gases.
These and other objects and advantages of the present invention will be better understood in view of the attached drawings and in light of the following detailed description of the invention.